Potassium ion-exchange on surface of beta-spodumene

DETAILED DESCRIPTION We claim: 1.
A method for producing a unitary glass-ceramic article of high strength wherein the crystal content thereof constitutes at least 50% by weight of the article with a surface compressive stress layer and an interior portion which comprises contacting a glass-ceramic article consisting essentially of Li.
sub.
2 O, Al.
sub.
2 O.
sub.
3, and SiO.
sub.
2, wherein the crystal phase therein consists essentially of beta-spodumene at a temperature between about 550.
degree.
-800.
degree.
C.
with a source of potassium ions for a period of time sufficient to replace at least part of the lithium ions of said beta-spodumene in a surface layer of the article with a corresponding amount of potassium ions, said replacement not changing the essential crystal structure of the beta-spodumene crystals to thereby effect a compressively stressed surface layer on the article.
2.
A method according to claim 1 wherein said time sufficient to replace at least part of the lithium ions of said beta-spodumene does not exceed about 16 hours.
3.
A method according to claim 1 wherein said glass-ceramic article is contacted with said source of potassium ions at a temperature between about 700.
degree.
-800.
degree.
C.
4.
A unitary glass-ceramic article of high strength wherein the crystal content thereof constitutes at least 50% by weight of the article with a surface compressive stress layer and an interior portion consisting essentially of Li.
sub.
2 O, Al.
sub.
2 O.
sub.
3, and SiO.
sub.
2, wherein the crystals of said interior portion consist essentially of beta-spodumene and the crystals of said surface compressive stress layer consist essentially of beta-spodumene, the crystal structure of said latter crystals being essentially unchanged but in at least a portion of which the proportion of lithium ions is less with a corresponding increase in an amount of potassium ions.




Description:
The manufacture of glass-ceramic articles contemplates the carefully controlled crystallization of a glass article in situ